Typical engine air cooled oil coolers of turbofan gas turbine engines, known as surface coolers, are provided with fins on the side facing the engine bypass airflow. The heat transfer density per cooler unit area is limited by the maximum fin height to reduce perturbations in the bypass duct, and by the air temperature in the bypass duct.
Accordingly, there is a need to provide an improved air-cooled oil cooler in gas turbine engines.